Subscriber access provided by Stockholm University Library
Characterization of Natural and Affected Environments
Stable isotopes and Bayesian modeling methods of tracking sources and differentiating bioavailable and recalcitrant phosphorus pools in suspended particulate matter Kristi A Mingus, Xiaomeng Liang, Arash Massoudieh, and Deb P. Jaisi Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b05057 • Publication Date (Web): 03 Dec 2018 Downloaded from http://pubs.acs.org on December 3, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 22
Environmental Science & Technology
1
Stable isotopes and Bayesian modeling methods of tracking sources
2
and differentiating bioavailable and recalcitrant phosphorus pools in
3
suspended particulate matter
4 5
Kristi A. Mingus1, Xiaomeng Liang2, Arash Massoudieh2, and Deb P. Jaisi1*
6 7 8 9
1Department 2Civil
of Plant and Soil Sciences, University of Delaware, Newark, DE 19716
Engineering Department, The Catholic University of America, Washington, DC 20064
10 11 12 13 14 15
* Corresponding authors: Deb Jaisi, Email:
[email protected], Phone: (302) 831-1376
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 ACS Paragon Plus Environment
Environmental Science & Technology
ABSTRACT
32 33
Page 2 of 22
Understanding the sources of different phosphorus (P) pools and their bioavailability under
34
imposed biogeochemical environments in a watershed is limited largely due to the lack of
35
appropriate methods. In this research, phosphate oxygen isotope ratios and Bayesian modeling
36
on fingerprinting elements were applied as two novel methods to identify sources and relative
37
recalcitrancy of particulate P pools suspended in water in the continuum of sources from land to
38
the mouth of a coastal estuary to the Chesapeake Bay. Comparative analyses of sizes, relative
39
ratios, and oxygen isotope values of particulate P pools in the creek water suggested that the
40
NaHCO3-P pool was bioavailable whereas NaOH-P and HCl -P pools were recalcitrant during P
41
transport along the creek. Agricultural field soil, streambank, and river bottom sediments were
42
major sources of particulate P and their contributions varied significantly at the headwater and
43
downstream regions of the creek. Bayesian modeling based on fingerprinting elements suggested
44
that tides played a major role in forming particulate matter from estuarine sources at the creek
45
mouth region and importing it upstream. These findings provide new insights into the origin and
46
fate of particulate P and the fidelity of isotope and fingerprinting methods in source tracking of P
47
in tidally influenced watersheds.
48 NaHCO3-Pi
NaOH-Pi
HNO3-Pi
24
Equilibrium
Recalcitrant particulate P Bioavailable particulate P
18OP (‰)
22
20
18
16
49
Creek flow direction A
C
F
G
H
I
J
J1
50 51
TOC Art
2 ACS Paragon Plus Environment
K
L
--
Page 3 of 22
Environmental Science & Technology
INTRODUCTION
52 53 54
Nutrient contamination of surface waters has long been a water quality challenge in major
55
rivers and coastal watersheds in the U.S. Surface water eutrophication and dead zones, for
56
example in the Chesapeake Bay and the Gulf of Mexico, caused by excess nutrients derived
57
largely from agriculture are frequently highlighted in news and reports1. Restoration of such
58
water bodies is complicated by the various nutrient sources, their temporally and spatially
59
variable inputs, and complex interactions affecting their occurrence, fate, and transport2. The
60
focus on water quality improvement has raised debates, and accountability for nutrient release
61
remains open-ended.
62
By virtue of the properties of the phosphate (PO43-) anion, which has high affinity for
63
solid surfaces such as soil minerals, particulate matter, and colloidal particles, phosphorus (P) is
64
transported dominantly in the particulate form3. Likewise, particulate phosphorus (PP) is the
65
dominant form of P exported by rivers to the Chesapeake Bay4. The particulate matter is made
66
up of both inorganic and organic components. The inorganic-rich components such as sand, silt,
67
and clay (aggregates) can settle in water at low flow whereas organic-rich components consisting
68
of phytoplankton, bacteria, and other biological materials typically remain floating5. Thus, the
69
composition and relative concentrations of inorganic P (Pi) and organic P (Po) of suspended
70
particulate matter often vary along a river transect, particularly in estuarine settings. Further,
71
differences in residence time and mobility of Pi and Po in the particulate matter cause variability
72
of their concentrations along river channels.
73
Scientific understanding of the role of PP in water quality remains severely limited. For
74
water quality assessment, the bioavailability of particulate matter, defined as the potential plant
75
or microbial uptake of a specific form of nutrient in a particular ecosystem6 from the point of
76
entry to the ecosystem to the point of export, should be known. However, determining the
77
bioavailability of PP pools in a system is not straightforward because they are impacted by site-
78
specific biogeochemical conditions such as salinity, pH, redox condition, and community
79
structure and activity of (micro)organisms. Methodological limitations are a major challenge in
80
determining P or PP bioavailability. For example, indirect methods commonly used to quantify
81
bioavailability include dissolved/soluble reactive P plus biomass P7, bioassays8, and sequential
82
extractions7, 9, 10. These operationally defined methods still provide useful information and allow 3 ACS Paragon Plus Environment
Environmental Science & Technology
83
comparisons among literature data but cannot be used to test if particular P pools are bioavailable
84
in a given space and time. Further, multi-scale interactions among PP pools and with dissolved P
85
in water and the interplay of physicochemical and biological reactions demand more innovative
86
techniques that go beyond operationally defined methods capable of discriminating bioavailable
87
pools from recalcitrant PP pools. The major research objectives of this study were to i) identify
88
the sources of particulate P pools in the East Creek watershed and ii) differentiate bioavailable
89
and recalcitrant inorganic PP pools along an environmental gradient under base flow conditions
90
from the source sites in the watershed to the mouth at the Chesapeake Bay. In this research
91
phosphate oxygen isotopes and multi-element sediment fingerprinting methods were used to
92
meet these objectives.
93 94
MATERIALS AND METHODS
95 96
Study Site and Collection of Soil, Sediment, and Waters from Creek and Other
97
Landforms. East Creek is a tidally influenced tributary located in Somerset County in
98
Maryland and it drains to the lower Chesapeake Bay (Fig. 1a). The upstream part of the
99
watershed includes agricultural farms and scattered poultry operations with a few forest patches.
100
The southern half of the watershed is primarily surrounded by wetland and remains partly
101
saturated during high tide and after rain events. A total of 14 sampling sites (from A to L, Figure
102
1a) along the salinity gradient were chosen, which span from a drainage ditch near agricultural
103
fields to the mouth of the creek at the Chesapeake Bay. From each site, 8–64 L of water was
104
collected to achieve sufficient particulate matter for chemical and isotope analyses under
105
baseflow (receding tide) conditions. Conductivity of water was measured using an EC meter
106
(Orion, Beverly, MA) and salinity was measured using a salinity test kit (LaMotte, Chestertown,
107
MA). Paired sediment cores were collected from selected water sampling sites using a suction
108
corer11. The top 2 cm of the core, which represents freshly settled particulate or eroded surface
109
matter and dominates P exchange with the water column, was chosen for further analyses.
110
Streambank sites (next to sites F, H, and J) were selected based on the water flow direction and
111
visible scour channels. After collection, water, sediment core, and streambank samples were
112
stored on ice and placed in coolers and transported to the laboratory for analyses.
4 ACS Paragon Plus Environment
Page 4 of 22
Page 5 of 22
Environmental Science & Technology
Soil samples were collected from major land use types including agricultural farms,
113 114
forested lands, and wetlands in the watershed. Sampling locations in different land use types and
115
land covers were selected based on current and past land use maps, aerial photographs, and site
116
visits. At least 20 sampling sites per land use/cover were collected and processed separately.
117
From each site, at least two samples were collected from the top-soil (0–5 cm) and composited
118
by thorough mixing. Poultry litter applied in the field was collected from the stockpile in the
119
field.
120 121
Processing Suspended Particulate Matter and Soils from Potential Source Sites.
122
Suspended particulate matter in each water sample was separated via centrifugation using
123
Stokes’s Law of settling (≥100 nm cut-off size for particulate matter and
